Synthesis of wafer-scale graphdiyne/graphene heterostructure for scalable neuromorphic computing and artificial visual systems

Abstract: Constructing a new topological structure with unique ordered channels for rapid potassiation kinetics is crucial to ameliorating the inherent drawbacks of carbon anodes, arising from the large K-ion radius, such as huge volume expansion, slow diffusion rate, and poor interfacial transfer dynamics. Herein, dihydrogen- and nitrogen/hydrogen-substituted rhombic graphynes (HH-rGY, NH-rGY) were synthesized through a mechanochemical cross-coupling method using specific D2h-symmetric tetrahalogenated organic molecules and alkynyl-containing calcium carbide as precursors. The pyridinic-N atoms in NH-rGY can efficiently manipulate electron distribution and tailor structural arrangement, endowing unique AA'-stacking mode with ordered vertical rhombic channels, board interlayer spacing of 4.1 A (1.16 times to that of HH-rGY), and negligible volumetric expansion (< 3%) during potassiation, which are investigated by experiments and theoretical calculations. Instead of a common capacitive-dominated storage mechanism, intercalation-dominated K-storage is verified in rhombic graphynes by quantitative kinetics analysis. Especially, the NH-rGY electrode delivers a reversible capacity of 230 mAh g-1 at 50 mA g-1 (90.2% after 500 cycles) and 97 mAh g-1 at 5 A g-1 and retains 146 mAh g-1 at 2 A g-1 after 5000 cycles, owing to outstanding structural stability and rapid in-plane and inter-layer K+ diffusion. This work proposes a universal mechanochemical cross-coupling synthetic methodology and brings new insight into the topological structure design of carbon skeletons for high-performance potassium storage.

Abstract: Conventional computing based on von Neumann architecture cannot satisfy the demands of artificial intelligence (AI) applications anymore. Neuromorphic computing, emulating structures and principles based on the human brain, provides an alternative and promising approach for efficient and low consumption information processing. Herein, recent progress in neuromorphic computing enabled by emerging two-dimensional (2D) materials is introduced from devices design and hardware implementation to system integration. Especially, the advances of hopeful artificial synapses and neurons utilizing the resistive-switching-based devices, 2D ferroelectric-based memories and transistors, ultrafast flash, and promising transistors with attractive structures are highlighted. The device features, performance merits, bottlenecks, and possible improvement strategies, along with large-scale brain-inspired network fulfillment, are presented. Challenges and prospects of system application for neuromorphic computing are briefly discussed, shedding light on its great potential for AI.

Abstract: Recent explorations of twist in bilayer graphene and the discovery of superconducting phases at certain magic angles have laid the groundwork for a new branch in materials science called twistronics. However, theoretical studies on twisted layered materials are impeded due to the computational expense associated with first-principles calculations. Empirical force field approaches that include anisotropic terms to describe interlayer interactions have come to the fore as excellent alternatives to deal with such a stumbling block. Taking a cue from such formulations, herein, we describe our pursuit of capturing the interlayer interactions in bilayer graphynes with atomistic empirical potentials. The choice of the potentials, namely the improved Lennard-Jones potential and Hod’s interlayer potential is motivated by the objective of bringing out the role of anisotropy explicitly. Empirical parameters for both the potentials are calibrated against dispersion-corrected DFT calculations that are performed to incorporate the stacking, sliding and twisting features of the bilayer configurations. Although the isotropic improved Lennard-Jones potential is able to describe the interlayer stacking of graphynes, it is inadequate to account for the interlayer twist properties. The reparametrized anisotropic Hod’s interlayer potential portrays the interlayer twisting energy profiles of the benchmark DFT calculations with reasonable accuracy. Our potential formulations can bestow impetus to research on homo- and hetero-bilayer structures of graphynes and other carbonaceous two-dimensional materials.

Abstract: A phototransistor in which electric charges are absorbed by colloidal quantum dots and circulated in graphene exhibits high values for gain, responsivity and specific detectivity.

Abstract: We have demonstrated a methodology to generate large area graphdiyne films with 3.61 cm2 on the surface of copper via a cross-coupling reaction using hexaethynylbenzene. The device based on graphdiyne films for measurement of electrical property is fabricated and shows conductivity of 2.516 × 10−4 S m−1 indicating a semiconductor property.

Abstract: The electronic properties of inorganic devices such as memristors can be used to simulate neurological behaviour. In particular, ionic and electronic effects in a silver sulphide device are now shown to mimic short- and long-term synaptic functions. Memory is believed to occur in the human brain as a result of two types of synaptic plasticity: short-term plasticity (STP) and long-term potentiation (LTP; refs 1, 2, 3, 4). In neuromorphic engineering5,6, emulation of known neural behaviour has proven to be difficult to implement in software because of the highly complex interconnected nature of thought processes. Here we report the discovery of a Ag2S inorganic synapse, which emulates the synaptic functions of both STP and LTP characteristics through the use of input pulse repetition time. The structure known as an atomic switch7,8, operating at critical voltages, stores information as STP with a spontaneous decay of conductance level in response to intermittent input stimuli, whereas frequent stimulation results in a transition to LTP. The Ag2S inorganic synapse has interesting characteristics with analogies to an individual biological synapse, and achieves dynamic memorization in a single device without the need of external preprogramming. A psychological model related to the process of memorizing and forgetting is also demonstrated using the inorganic synapses. Our Ag2S element indicates a breakthrough in mimicking synaptic behaviour essential for the further creation of artificial neural systems that emulate characteristics of human memory.

Abstract: Combining the electronic properties of graphene(1,2) and molybdenum disulphide (MoS2)(3-6) in hybrid heterostructures offers the possibility to create devices with various functionalities. Electronic logic and memory devices have already been constructed from graphene-MoS2 hybrids(7,8), but they do not make use of the photosensitivity of MoS2, which arises from its optical-range bandgap(9). Here, we demonstrate that graphene-on-MoS2 binary heterostructures display remarkable dual optoelectronic functionality, including highly sensitive photodetection and gate-tunable persistent photoconductivity. The responsivity of the hybrids was found to be nearly 1 x 10(10) A W-1 at 130 K and 5 x 10(8) A W-1 at room temperature, making them the most sensitive graphene-based photodetectors. When subjected to time-dependent photoillumination, the hybrids could also function as a rewritable optoelectronic switch or memory, where the persistent state shows almost no relaxation or decay within experimental timescales, indicating near-perfect charge retention. These effects can be quantitatively explained by gate-tunable charge exchange between the graphene and MoS2 layers, and may lead to new graphene-based optoelectronic devices that are naturally scalable for large-area applications at room temperature.

Abstract: Structural remodelling of synapses and formation of new synaptic contacts has been postulated as a possible mechanism underlying the late phase of long-term potentiation (LTP), a form of plasticity which is involved in learning and memory Here we use electron microscopy to analyse the morphology of synapses activated by high-frequency stimulation and identified by accumulated calcium in dendritic spines LTP induction resulted in a sequence of morphological changes consisting of a transient remodelling of the postsynaptic membrane followed by a marked increase in the proportion of axon terminals contacting two or more dendritic spines Three-dimensional reconstruction revealed that these spines arose from the same dendrite As pharmacological blockade of LTP prevented these morphological changes, we conclude that LTP is associated with the formation of new, mature and probably functional synapses contacting the same presynaptic terminal and thereby duplicating activated synapses